1. Field of the Invention
The present invention relates to a storage apparatus used for a computer or a peripheral equipment of a computer, and specifically relates to an improvement in a servo mechanism for controlling positioning of a head for record and regeneration.
2. Description of the Prior Art
FIG. 1 is a side view showing a general magnetic disk apparatus, for example, as described in the Japanese Patent Laid-Open No. Sho-101777/1985.
In FIG. 1, Numeral 1 designates a support bed serving as a base, and a rotary apparatus 2 consisting of a spindle motor is fixed onto the surface of the support bed 1, and a disc-shaped recording medium 3 consisting of a magnetic disk is supported by a rotary shaft 2a of the rotary apparatus 2.
Facing the lower surface (recording surface) of the recording medium 3, a head 4 for recording information on the recording surface of the recording medium 3 or for regenerating information on the recording surface of the recording medium 3 is disposed in the state of being connected to a pressure spring 5 for forcing it to the recording surface. The pressure spring 5 is supported by an arm 6 so that the end thereof on the opposite side of the head 4 is put on one end of the arm 6. The other end of the arm 6 is fixed to a carriage 8 being one of constituent members of an actuator 7 as described later. As a result, the head 4 is affected by an energizing force of the pressure spring 5 and a buoyancy generated attending on rotation of the recording medium 3, and thereby it is moved in the radial direction of the recording medium 3 integrally with the actuator 7 (carriage 8) in the state of having a minute air gap with the recording medium 3, and the position thereof is controlled. The actuator 7 is composed of a bearing 9 for guide-moving the carriage 8 on the support bed 1, a cylindrical coil 10 provided around one end of the carriage 8, a magnet 11 disposed opposite to the coil 10 and a yoke 12 for positioning the magnet 11 in addition to the carriage 8.
Numeral 13 designates a position sensor for detecting the position of the actuator 7 in the radial direction of the recording medium 3, and the position sensor 13 is composed of a converter 14 fixed on the support bed 1 and an optical linear scale 15 provided in the carriage 8.
FIG. 2 is a block diagram showing a storage apparatus wherein a control driving part is added to the magnetic disk apparatus as shown in FIG. 1.
In FIG. 2, numeral 19 designates a computer, and the computer 19 outputs a movement-positioning command to a servo circuit 17, and outputs a record command or a regeneration command to a read/write circuit 18. Being inputted the movement-positioning command from the computer 19, the servo circuit 17 inputs positional information from the position sensor 13 and positioning speed information from a speed demodulator 16 for detecting the positioning speed of the head 4 by differentiating and shaping the positional information from the position sensor 13, and drives the actuator 7 to set the head 4 in a proper position according to these information.
Being inputted a record command or a regeneration command from the computer 19, the read/write circuit 18 writes information on the recording medium 3 through the head 4, or reads out information from the recording medium 3.
Next, description is made on operation of the storage apparatus having such a configuration.
When the recording medium 3 is rotated attending on rotation of the rotary apparatus 2, the buoyancy is generated in the head 4 by a viscous air flow over the surface of the recording medium 3. The buoyancy is balanced against the energizing force of the pressure spring 5, and thus the recording medium 3 rotates while having the minute air gap with the head 4.
When a movement-positioning command is outputted from the computer 19 to the servo circuit 17, a current flows through the coil 10, and a force according to the Fleming's left-hand law acts on a magnetic circuit composed of the magnet 11 and the yoke 12. Then, the carriage 8 is driven in the radial direction of the recording medium 3, and the head 4 is moved to be positioned while making seek operation on information tracks arranged in the radial direction at predetermined intervals on the concentric circles of the recording medium 3. At this time, the servo circuit 17 positions the head 4 at a command position according to the positional information from the position sensor 13.
After completing movement-positioning of the head 4, a record command or a regeneration command is outputted from the computer 19 to the read/write circuit 18, and the head 4 records information on the recording medium 3, or regenerates information from the recording medium 3.
In addition, positioning of the head 4 is performed by a servo mechanism composed of the servo circuit 17, the actuator 7, the position sensor 13 and the speed demodulator 16 according to a general theory of automatic control.
It is well known that a gain margin of several dB is required for a stable operation of the servo mechanism. In the conventional storage apparatuses, the actuator 7 and the positions sensor 13 are configurated by assembling machine parts therewith, and therefore a mechanical resonance generated due to deviations in parts or in assembling them makes no gain margin left, and resultingly the servo mechanism becomes unstable and causes an oscillation, and thus there has been a problem that positioning of the head 4 cannot be made.